Dominant is neither major or minor, but a sound quality all of its' own. There are 5 sound qualities we use to describe everything in music; Major, Minor, Dominant, Augmented, and Diminished. So we could have.......
Cmaj7, Cmin7, C7, Caug, Cdim7
Here's the difference
Cmaj7...CEGB
Cmin7....CEbGBb
C7 (dominant)..CEGBb
Caug..CEG#
Cdim7..CEbGbA
Dominant chords are the primary chords used for blues...although you will find the other chord qualities used in other forms of blues. There is like 8 progressions that all of Blues music is based off of.